As mentioned above, this is probably the classic text on Gestalt Therapy written by perhaps its most famous practitioner Fritz Perls, with help from others. Perls was notorious for hating abstraction and theorizing, yet here comes over as a brilliant therorist in addition to being a charismatic therapist.
There are theoretical discussions in this book on how the psyche is viewed in the Gestalt Approach, and Perls is largely non-partisan in this when looking at the applicablity of certain rival theories. He is broadly fair to Freud's achievement in the creation of therapy, without completely going along with everything. He is similarly fair to other such as Jung, Karen Horney and Wilhelm Reich, though there is not as much discussion of them. The text inevitably concentrates on his own approach.
The style is scholarly, but certainly not unreadable. There are a number of practical exercises which might help someone, in therapy or not, to become more aware of their mind and body, with testamonies form clients / patients who have benefitted from their use. In the second half, Perls looks Gestalt theroies of self and various mechanisms observed in the psyche. All of this makes for fascinating reading
This book is essential for Gestalt practitioners, and counselling students. Though book is clear and well written, it is perhaps not ideal for beginners. However, that is not a criticism. This book is probably meant for a more advanced audience. For those new to Gestalt and Perls that I would recommend the wonderful and lively
Gestalt Therapy Verbatim, which is a transcript of his workshops at Esalen. All the same there are rich pickings in this volume for anyone regardless of theraputic approach.